helium mass spectrometer leak detector system for electric vacuum device

At present, the commonly used reference leak in helium mass spectrometer leak detector system is thin-film helium leakage. The standard leak of 10-8 PA · m3 / S is generally used to calibrate the low-order leakage rate of 10-10 PA · m3 / s. The quantitative results of leak detection are more reliable if the leakage rate of different orders of magnitude is used for calibration in a wide range. However, the helium leakage hole with fixed leakage rate can only calibrate the sensitivity of the instrument itself, that is to say, it reflects the minimum leakage rate that can be detected by an instrument, method or system under specific conditions, that is, the leak detection sensitivity. The actual leak detection level not only depends on the instrument itself, but also has a great relationship with the tested system and leak detection method.

For example, when the diverter pump or accumulation method is used, the minimum detectable rate will be higher or lower. Therefore, it is necessary to distinguish the sensitivity calibration of leak detector and the sensitivity calibration of leak detection. The leak detection sensitivity qmin refers to the minimum leakage rate that the helium mass spectrometer leak detector and leak detection system can detect when pure leak gas passes through the leak hole under specific working conditions. In the leak rate test, the standard leak is used to calibrate the leak detection sensitivity of the system.

Preparation for helium leak detection of electric vacuum devices

1. Environmental requirements for vacuum leak detection

The best operating temperature: 15 ~ 30 ℃, humidity ≤ 70 RH. The leak detection environment should be clean and well ventilated (eliminate the helium content in the air, the helium concentration is too high, and the output helium signal of the instrument is unstable), the air flow is stable, and there is no strong electromagnetic interference and strong vibration. Temperature, humidity and atmospheric pressure monitoring devices should be provided on site.

2. Air vent leak detector

According to the structural characteristics and load-bearing requirements of the electric vacuum device, a reasonable leak detection platform is designed and manufactured, which is sealed with the leak detection port of the leak detector. The workpiece to be inspected can be placed on the leak detection platform with the help of the sealing die. The leak detection port 1 is sealed with a rubber plug, and the leak detection can be carried out after vacuumizing through the leak detection port. For the parts with overload weight or a few special structures that cannot be placed on the leak detection platform, the air tightness test can be carried out through the leak detection port. In other words, the vacuum rubber pipe is used to connect the leak detection port and the inspected part. The leak detection port 2 is sealed with a blind plate or a rubber plug. After the leak detector is vacuumed, the leak detection can be carried out on the inspected workpiece. The load-bearing capacity of the designed leak detector is less than 30 kg, which can make the tested parts with different sizes use different diameter and shape sealing mould for vacuum sealing, so as to realize the vacuum tightness detection.

3. Instrument calibration and sensitivity testing

GB / t13979 requires the instrument to be calibrated, and the calibration leakage shall be sent to the measuring institution for recalibration at regular intervals, and the inspection period shall not exceed 2 years. The default internal auto calibration of helium mass spectrometer leak detector is set to on. Therefore, the leak detector will be automatically calibrated when it is turned on. If the calibration fails, it is necessary to check the cause of the failure and eliminate the failure. If it is found that the reaction capacity of the leak detector is not good, it needs to be calibrated in time. However, when the minimum detectable rate of the re calibration increases to more than 65% of the minimum detectable rate, or the indication value after normal operation adjustment is still lower than the nominal value of the calibrated leak, the sensitivity of the leak detector decreases. The reading of leakage rate is low. The leak detector should be cleaned, repaired or recalibrated.

4. Inspected parts and leak detection mould

Before the leak detection, the oil dirt and dirt on the surface of the parts to be inspected shall be removed, and the high temperature degassing treatment shall be carried out. The purpose is to prevent the leakage hole from being blocked by dirt, oil, organic solvent, etc., and the pump and pipeline of the leak detector will not be polluted, so as to avoid the impact of the workpiece gas on the leakage detection results. The mould for leak detection shall be free from deformation and kept dry and clean.